Many computer systems use magnetic disk drives for mass storage of information. Magnetic disk drives typically include one or more sliders having a read head and a write head. An actuator/suspension arm holds the slider above the surface of a magnetic disk. When the disk rotates, an air flow generated by the rotation of the disk causes an air bearing surface (ABS) side of the slider to fly at a particular height above the disk. As the slider flies on the air bearing, a voice coil motor (VCM) moves the actuator/suspension arm to position the read/write head over selected tracks of the disk. The read/write head may then read data from or write data to the tracks of the disk.
A typical write head includes a main write pole and a return pole. The main write pole has a yoke portion and a pole tip portion. The pole tip extends from the ABS of the write head to the yoke of the write pole. The point where the pole tip meets the yoke is referred to as the flare point. The point where the yoke begins has a trapezoidal shape that flares outwardly from the pole tip. The yoke of the main write pole then connects to the return pole through a back gap. A coil wraps around the yoke or the back gap to provide the magnetic flux used for the write operation. The width of the pole tip controls the track width that is written by the recording head, so the width of the pole tip is preferably small (i.e., less than 100 nanometers).
Write heads and other components of the slider are typically produced using thin-film deposition and patterning techniques. Material layers which make up a write head for a slider are typically formed by depositing full film materials of the main write pole layers on a non-magnetic layer (e.g., alumina), depositing and patterning a masking layer over the main write pole layers to form a mask structure, etching the exposed portion of the main write pole layers around the mask structure to define a pole tip and a flare point of the write pole, and then removing the mask structure. A trailing shield or a wrap around shield may then be formed around the pole tip. A shield is formed to prevent the main write pole from inadvertently writing to neighboring tracks. The use of bi-layer wrap around shields increases the write field gradient of the main write pole when the shield comprises a lower magnetic moment outer layer surrounding a higher magnetic moment inner layer proximate to the main write pole. The increased write field gradient yields sharper magnetic transitions on the disk and therefore, improves the signal to noise ratio of the disk.
After the read/write heads are formed, the sliders are cut from the wafer into individual sliders, or rows of sliders. The surfaces of the sliders that are exposed when the wafers are cut will eventually form the air bearing surface (ABS) of the slider.
A lapping process is used to form the ABS of a slider, and more particularly, the ABS of the write head. Lapping removes material from the ABS of the slider until specific design parameters of the write head are reached, such as a desired throat height of the wrap around shield. The throat height is a distance between the ABS of the slider and the back edge of the shield. Problems arise, however, when lapping removes materials on the ABS of the slider at different rates. Different materials, such as high and low magnetic moment materials used in fabricating the bi-layer wrap around shields, have different removal rates. More specifically, the high magnetic moment material used for the inner layer of the wrap around shield typically is removed at a lower rate than the lower magnetic moment material used for the outer layer of the shield. This results in the high moment inner layer protruding from the ABS above the other layers on the ABS. This protrusion reduces the clearance for the slider during disk operation, and therefore, increases the potential for head to disk contact. Thus, an ongoing need exists for improving write heads that include bi-layer wrap around shields.